1. Field of the invention
The present invention relates to a rotation control apparatus for controlling a rotating state of a motor such as a spindle motor for rotating an optical disk or the like.
2. Description of Background Information
Hitherto, rotation control of a motor such as a spindle motor has been performed by using a sync signal (synchronization signal) recorded on an optical disk, for example, at predetermined intervals together with information data to be reproduced, so that the sync signal corresponds to such information data. The sync signal is detected, and the periodic intervals at which the sync signal is detected are compared with a reference signal having a predetermined constant period (the period is set at a value at which the recorded information is reproduced in the best state when the optical disk or the like is rotated according to that period). The rotational speed of the motor is controlled so that a difference between them is equal to zero, namely, the period of the sync signal detected coincides with the period of the reference signal.
In conventional rotation control apparatuses briefly described above, it is however a prerequisite that the sync signal is recorded at predetermined constant intervals (period). In the case of an optical disk or the like having such a structure wherein parts of the sync signal are recorded at intervals different from those of the other sync signal parts, with the conventional rotation control apparatus and phase sync circuit, it is impossible to maintain an accurate rotating state such as the CLV (Constant Linear Velocity) or CAV (Constant Angular Velocity) type rotation.
More particularly, if the conventional rotation control apparatus is applied to the optical disk or the like such that parts of the sync signal are recorded at an interval corresponding to a period different from the period of the other sync signal parts, even the interval of the sync signal parts different from the intervals of the other sync signal parts is also controlled so as to be matched with the period (corresponding to the intervals of the other sync signal parts) of the reference signal. When the portion where the interval of the sync signal parts is different from the intervals of the other sync signal parts is detected, therefore, the rotational speed is deviated (being faster or delayed) from the rotational speed to be obtained by a value corresponding to the difference between the intervals of the sync signal. Namely, there arises a problem that the operation to control the rotation at the period of the reference signal contrarily causes a fluctuation of the rotation.